Well I would say buy a V-8 with a 5-Speed. If you have the $$$$ that is. If it is slim pickins where you live for stangs than broaden your search area. Maybe take a road trip with a friend or a train. Then drive the beast back! If you dont have the $$$$, the buy a 4 cylinder with whatever trans you desire. Keeping in mind that the auto is easy to switch over. I just completed a 2.3l (auto) swap on my 87 LX hatch. I put in a 93 5.0 engine (auto). Swapping pedal sounds like a major pain and if you dont have the know-how then I suggest you dont go through the trouble. Also budget about 2 times as much man hours than you are expecting. I did my swap for about $1500. Bought the motor/trans for $1300 along with EVERYTHING. It took me 4 1/2 months to do. That was in my spare time of course. By the way, the 4 cylinder 5 speed will not work that well with a 5.0 engine because the spline shafts are different. It may work for a month untill it craps out. If you have any more questions than feel free to email me because I think I know everything there is to know about the 2.3 to 5.0 swap.!!
Good luck!